1. Field of the Invention
The present invention relates to apparatus for detecting the presence of water in a fuel tank and, more particularly, to circuitry for indicating the fuel level in a fuel tank and for simultaneously signaling the presence of water in such fuel tank.
2. Description of the Prior Art
It is well known that water accumulates over a period of time in fuel tanks as a result of condensation, especially in tanks used to store fuel. It is also well known that the presence of water in fuel, especially in diesel fuel, in very undesirable. In the best of cases, the presence of water in fuel will effect engine performance. In the worst of cases, the water will cause the engine to malfunction.
The most common technique used in an attempt to solve the problem of water in fuel is to provide a filter in the fuel line. Unfortunately, such filters have limited capacities and if any significant amount of water is present in the fuel, such capacity will soon be reached, permitting the water to pass with the fuel to the engine.
Since water is heavier than fuel, it will lay on the bottom of a fuel tank. This being the case, it is very common, such as in fuel tanks for airplanes, to provide a sump in the bottom of a tank and to bleed the water from this sump periodically. Unfortunately, none of these techniques are totally satisfactory and they have no capability of signaling the presence of water in a fuel tank.
It is also becoming quite common to use capacitive type fuel gauges to determine the liquid level in a tank. Fuel gauges of this type are described in my prior U.S. Pat. Nos. 4,145,927 and 4,201,085. Such systems include a pair of parallel plates having a generally vertical orientation so that as the liquid rises in the tank, an increasing area of the plates is adjacent to the liquid. The change in capacitance between the plates as a function of liquid level is utilized to generate an electrical signal indicative of liquid level.
While such a system is highly effective, it is also highly sensitive to the presence of water in a fuel tank. That is, diesel fuel and gasoline both have a dielectric constant of about 2, whereas water has a dielectric constant of about 80. Thus, the presence of water in the fuel will significantly effect the capacitance between the plates and will severely effect the liquid level indication. Again, no means has been available heretofore for signaling the presence of water in a fuel tank.